This invention relates to improvements in the original log feeding system of U.S. Pat. No. 4,009,632, and to a sawing method which is used both in the original system and the improved apparatus.
Prior to the development of the original log feeding system developed by the present inventor, there had been no uncomplicated and effective commercial systems for engaging logs and advancing them accurately through a saw.
As pointed out in the specification of my earlier application, prior skrag saws were operated by placing a log on a narrow chain provided with pusher dogs for driving the logs through circular saws or opposed band saws. On the outfeed side of such saws, upright guides called "splitters", were positioned in the cut made by the saw blade. Although simple, the use of these systems for accurate sawing was restricted to operation on essentially cylindrical small short logs.
There have been prior systems in which logs of varying lengths could be accurately sawed by engaging their opposite ends with members which apply a gripping force thereto. Such systems are disclosed in U.S. Pat. Nos. 3,503,428 and 3,731,578 to Bo Ingemar Ackerfeldt. Such systems are highly complicated and far more complex and expensive than the original system and improved apparatus of the present inventor. Ackerfeldt suspends the forward and rear log-engaging means from a common overhead track. Both log-engaging means are coupled to and disengagable from a common drive cable, and a spring is used to apply a gripping force between the log-engaging means.
During the prosecution of the original patent application, it was learned that Mead et al U.S. Pat. No. 2,332,654 disclosed a system for advancing transversely oriented boards towards a saw by pusher members on a driven chain, while simultaneously imposing a rearward force on the boards by holdback members supported on a frictionally retarded carrier chain. The differences between my original apparatus and the Mead et al apparatus are claimed in the original patent. The differences between the method of operation of my original and present apparatus and that of the Mead et al patent is the subject of the method claimed herein. The present apparatus also includes a number of improvements which have been developed subsequent to the filing of the patent application on the original system.
A basic principle of operation common both to the original apparatus and the present improved apparatus is the method of operation wherein the rear end of a log is engaged by a rear member driven in a forward direction, and the forward end of the log is engaged by a forward member which is driven forwardly by the moving log but resists such forward movement. This exerts a rearward force on the log, causing the log to be gripped firmly between the forward and rear members as it is advanced substantially along its longitudinal axis through the saw. For convenience of expression, but without limitation to any structure disclosed herein, the forward and rear members will be referred to respectively as holdback dogs and pusher dogs.
This basic principle of operation results in the positive clamping of the log and assures its straight and accurate travel through the saw. It permits any unit to handle logs having a wide range of lengths and, when vertical adjustability of one of the dogs is provided, it permits a unit to handle logs having a wide range of diameters.
An improved feature of the present apparatus is that, prior to engagement by the dogs, the log is located on an initial support which permits or causes the log to be pre-oriented, i.e. moved to displaced positions offset laterally and/or angularly with respect to the machine axis. Taper sawing may be performed when the longitudinal axis of the log is angularly inclined to the machine axis; and, offset sawing results when the longitudinal axis of the log is parallel to and offset laterally from the machine axis. In both instances, it is preferred that the log axis be substantially horizontal and substantially parallel to the machine axis. In this context, "substantially" means within about five degrees of the machine axis.
One structural feature of the improved apparatus which facilitates the pre-orientation of a log is that the holdback dog is supported and mounted on a carrier which lies forwardly of the initial log support and is located below the path of the log moving through the saw. Preferably, this carrier is an endless chain from which the holdback dogs project upwardly while engaging a log. This arrangement also avoids the movement of a dog-carrier between or through the initial log support as in the original apparatus; and, it makes it possible to equip the apparatus with a bottom-flattening chipper head which operates on a log moving toward the saw.
Another improvement over the original apparatus is the simplification which has resulted from shortening the effective path followed by the pusher dogs while engaging a log, thus eliminating a portion of the structure required for supporting and guiding the pusher dogs. This is achieved by supporting and guiding the holdback dogs below the log path, and supporting and guiding the pusher dogs above the log path. In conjunction with this, it is desirable to add rotary driven members for frictionally engaging the sawn logs to move them along the machine axis for discharge.